Integrated bondline spacers for wafer level packaged circuit devices

ABSTRACT

A method of forming a wafer level packaged circuit device includes forming a device wafer, the device wafer including a first group of one or more material layers left remaining in a first region of a substrate of the device wafer; and forming a cap wafer configured to be attached to the device wafer, the cap wafer including a second group of one or more material layers left remaining in a second region of a substrate of the cap wafer; wherein a combined thickness of the first and second groups of one or more material layers defines an integrated bond gap control structure upon bonding of the device wafer and the cap wafer.

BACKGROUND

The present disclosure relates generally to semiconductor devicemanufacturing and, more particularly, to bond gap control structures(BGCS) for wafer level packaged optical microelectromechanical systems(MEMS) devices.

Microelectromechanical systems (MEMS) are integrated micro devices orsystems combining electrical and mechanical components. MEMS devices maybe fabricated using, for example, standard integrated circuit batchprocessing techniques. Exemplary applications for MEMS devices includesensing, controlling, and actuating on the micro scale. Such MEMSdevices may function individually or in arrays to generate effects on amacro scale.

Many MEMS devices require a vacuum environment in order to attainmaximum performance. The vacuum package also provides protection and anoptimal operating environment for the MEMS device. Specific examples ofthese MEMS devices include infrared MEMS such as bolometers, and certaininertial MEMS such as gyros and accelerometers. Previously, MEMS deviceshave been individually packaged in vacuum compatible packages afterfabrication and dicing of the MEMS device. Often, however, the cost ofpackaging MEMS devices in traditional metal or ceramic packages may beon the order of about 10 to 100 times the device fabrication cost. Thisespecially true if a vacuum is required in the package. These highpackaging costs therefore make it difficult to develop commerciallyviable vacuum packaged MEMS devices. In addition, MEMS devices arefragile especially after dicing. Care must be taken in handling thesedevices, and traditional integrated circuit fabrication machinery cannotadequately handle and protect MEMS devices. Thus, special handlingtechniques have also been developed to protect the MEMS devices untilvacuum packaging has been completed. These special handling proceduresalso add additional cost to the production of MEMS devices.

Wafer Level Packaging (WLP) was developed to address the high cost ofpackaging of MEMS by eliminating the traditional packages. In the WLPprocess, two semiconductor wafers may be bonded together using a joiningmaterial to yield bonded wafers. For example, a device wafer may bebonded to a lid wafer using an adhesive or solder to form a packagedMEMS device. Certain applications may require that the joining materialform a substantially uniform bond line. In certain situations,substrates (such as silicon wafers) may be bonded together using ajoining material. After bonding, the joining material forms a bond linein between the substrates. However, the uniformity of the bond line maybe affected by the flatness of the substrates and the uniformity of thebond force used to bond the wafers. The uniformity of the bond line maybe controlled by placing spacers at certain intervals across the surfaceof one or both substrates. However, adding the spacers usually requiresadding process steps to the fabrication process.

SUMMARY

In an exemplary embodiment, a method of forming a wafer level packagedcircuit device includes forming a device wafer, the device waferincluding a first group of one or more material layers left remaining ina first region of a substrate of the device wafer; and forming a capwafer configured to be attached to the device wafer, the cap waferincluding a second group of one or more material layers left remainingin a second region of a substrate of the cap wafer; wherein a combinedthickness of the first and second groups of one or more material layersdefines an integrated bond gap control structure upon bonding of thedevice wafer and the cap wafer.

In another embodiment, a method of forming a wafer level packagedcircuit device includes forming a device wafer, the device waferincluding a polyimide layer formed in a first region of a substrate ofthe device wafer, and a first solder metal stack layer formed on thepolyimide layer, wherein the polyimide layer is a same polyimide layerthat is also used in the formation of microelectromechanical systems(MEMS) devices of an integrated circuit on the device wafer, and thefirst solder metal stack layer is also a same first solder metal stacklayer used to form a sealing ring for the device wafer; forming a capwafer, the cap wafer including an antireflective coating layer formed ina second region of a substrate of the cap wafer, and a second soldermetal stack layer formed on the antireflective coating layer, whereinthe antireflective coating layer is a same antireflective coating layerthat is also formed on a cavity portion of the cap wafer, and the secondsolder metal stack layer is also a same second solder metal stack layerused to form a sealing ring for the cap wafer; and bonding the cap waferto the device wafer, thereby defining an integrated bond gap controlstructure comprising the polyimide layer, the first solder metal stacklayer, the second solder metal stack layer, and the antireflectivecoating layer. If a getter is used in the package, it may also beincluded in the BGCS structure described above.

In another embodiment, a wafer level packaged circuit device includes adevice wafer bonded to a cap wafer. The device wafer includes apolyimide layer formed in a first region of a substrate of the devicewafer, and a first solder metal stack layer formed on the polyimidelayer, wherein the polyimide layer is a same polyimide layer that isalso used in the formation of an integrated circuit on the device wafer,and the first solder metal stack layer is also a same first solder metalstack layer used to form a sealing ring for the device wafer. The capwafer includes an antireflective coating layer formed in a second regionof a substrate of the cap wafer, and a second solder metal stack layerformed on the antireflective coating layer, wherein the antireflectivecoating layer is a same antireflective coating layer that is also formedon a cavity portion of the cap wafer, and the second solder metal stacklayer is also a same second solder metal stack layer used to form asealing ring for the cap wafer; and an integrated bond gap controlstructure (BGCS) disposed between the device wafer and the cap wafer,the integrated BGCS comprising the polyimide layer, the first soldermetal stack layer, the second solder metal stack layer, and theantireflective coating layer.

In another embodiment, a method of forming a wafer level packagedcircuit device includes forming a device wafer; forming a cap wafer;forming, on either the cap wafer or the device wafer, a bond gap controlstructure comprising one or more material layers used in the formationof either the cap wafer or the device wafer, and left remaining in aregion of a substrate of either the cap wafer or the device wafer; andbonding the cap wafer to the device wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts:

FIG. 1( a) illustrates a top down acoustic image of a bonded pair ofwafers without a BGCS showing the results of nonuniformity of the bondline;

FIG. 1( b) is a side cross sectional view of a bonded pair of waferswithout a BGCS showing nonuniformity of the bond line, and causingsolder to flow outside a specified bond region;

FIG. 2 is a top view of a patterned side of an exemplary cap wafer thatmay be used in accordance with the teachings herein;

FIG. 3 is an enlarged top view of a patterned side of an exemplary capwafer that may be used in accordance with the teachings herein;

FIG. 4 is a side cross sectional view of a portion of a device wafer tobe bonded to a corresponding portion of a cap wafer that results in theformation of integrated BGCSs, in accordance with an exemplaryembodiment;

FIG. 5 is a side cross sectional view illustrating bonding of the deviceand cap wafers of FIG. 4;

FIG. 6 is a side cross sectional view of a portion of a device wafer tobe bonded to a corresponding portion of a cap wafer that results in theformation of integrated BGCSs, in accordance with another exemplaryembodiment;

FIG. 7 is a side cross sectional view illustrating bonding of the deviceand cap wafers of FIG. 6;

FIG. 8 is a top view illustrating the placement of a vacuum getter layeratop the solder base metal layer of the cap wafer in the embodiment ofFIGS. 6 and 7;

FIG. 9 is a cross sectional, perspective view illustrating the placementof the vacuum getter layer atop the solder metal layer of FIG. 8;

FIG. 10 is a side cross sectional view of a portion of a device wafer tobe bonded to a corresponding portion of a cap wafer that results in theformation of integrated BGCSs, in accordance with another exemplaryembodiment;

FIG. 11 is a side cross sectional view illustrating bonding of thedevice and cap wafers of FIG. 10;

FIG. 12 is a side cross sectional view of a portion of a device wafer tobe bonded to a corresponding portion of a cap wafer that results in theformation of integrated BGCSs, in accordance with another exemplaryembodiment; and

FIG. 13 is a side cross sectional view illustrating bonding of thedevice and cap wafers of FIG. 12.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures and components have notbeen described in detail so as not to obscure the related relevantfeature(s) being described. Also, the description is not to beconsidered as limiting the scope of the embodiments described herein.

As indicated above, infrared MEMS devices and certain other inertialMEMS devices require a vacuum environment to attain maximum performance.For example, infrared microbolometers require an operating pressure ofless than 10 millitorr (mT) to minimize thermal transfer from thedetector elements to the substrate and package walls. Thus, vacuumcompatible materials processes and equipment must be used. Infrareddevices also require an optically transparent cover. These packagingrequirements translate to high labor and capital expense and present asignificant cost barrier to commercially viable MEMS devices.Traditional MEMS device packaging costs can be ten to one hundred timesthe basic device fabrication cost even in reasonably high volume.

A solution to high packaging costs is to eliminate the traditionalindividual vacuum packaging of a completed die. More specifically, thisis achieved by moving the packaging step into the wafer fabricationarea. A cap wafer is aligned and mounted to the device wafer with anannular seal ring of solder, or other sealing material, forming anenclosed cell at each die location. This cap attachment process iscompleted in a vacuum environment, leaving each MEMS device in a vacuumcell. Interconnects are brought out under the solder seal ring and areisolated by a dielectric layer.

FIG. 1( a) illustrates an image of a bonded pair of wafers 100. Whenbonding two wafers together, regardless of whether the joining materialis solder, adhesive, or some other intermediates, the flatness of thesubstrates and the amount and uniformity of bond force largely determinethe bond line geometries in terms of gap (thickness) and width. Asillustrated in the circled regions 102, the bonded wafer pair 100exhibits bond width and gap uniformity issues in the absence of a bondgap control structure or spacer (BGCS). As further depicted in the sidecross sectional view of FIG. 1( b), the bonded pair of wafers 104, 106,without a BGCS further results in causing solder 108 to flow outside aspecified bond region.

A BGCS may serve as a mechanical stop that controls the thickness of abond line between two surfaces joined by solder, adhesive, or otherjoining material, and also prevents the joining material from spreadingin an undesired manner. In certain embodiments, a BGCS may be disposable(i.e., may be removed during wafer dicing). If the BGCS is formed frommaterials that are not otherwise used in the formation of either the capwafer or the device wafer (e.g., a polyimide or other material), thenthis results in additional processing steps. Any additional process orprocesses can in turn increase the risk of adding contamination in theform of particles or chemical residues to the optical window surfacesthat are difficult to clean.

Accordingly, in the present embodiments, existing layers used in theformation of an integrated circuit wafer (e.g., an infrared (IR)detector) and/or a cap wafer can now also be advantageously used in theformation of bond gap spacers. Rather than forming additional layers oncompleted device and cap wafers, the package fabrication process mayeasily be modified to leave small regions of these layers to formspacers of the materials that are already integral to the process. In sodoing, the present embodiments eliminate a separate spacer forming stepin the cap wafer fabrication, which in turn involves spraying orspinning a separate layer of polyimide material (for example) on thewafer, photo-patterning the spacers, baking the material to harden it,and removing all residual traces from the optical surfaces. Further,this approach also eliminates a possible need for capital equipment forthe spray deposition of the polyimide, as it is often not compatiblewith photoresist dispensing equipment. Still another advantage is thesimplification of the packaging process and enhancement of product yieldby reducing risk of leaving residue on optical surfaces. Residue andparticles are a prime caused of rejection for optical failures, andorganic residue in the package is a prime cause of loss due to poorvacuum and shortened product life.

Referring now to FIG. 2, there is shown a top view of a patterned sideof an exemplary cap wafer 200 that may be used in accordance with theteachings herein. The cap wafer 200 may, in one embodiment include asilicon substrate 202, although any suitable wafer substrate materialmay be used. The cap wafer 200 includes a plurality of cap sealing rings204 corresponding in number to device sealing rings on an integratedcircuit device wafer (not shown in FIG. 2). Each of the cap sealingrings 204 corresponds to a device sealing ring so that the cap wafer 200mates with a device wafer. Cavities 206 and bonding pad channels 208 areformed in the cap wafer 200 using an appropriate process such as wet ordry etching.

The cavities 206 provide an increased volume for a vacuum packaged MEMSdevice (not shown in FIG. 2), which in turn provides for a lower vacuumpressure level within the vacuum cell. The bonding pad channels 208 maybe used to provide clearance over bonding pads (not shown in FIG. 2) sothat a dicing saw, etching process, or other suitable process may beused in a later step to open the lid wafer to expose the bonding padsfor device testing before dicing of the wafer.

As further depicted in FIG. 2, the cap wafer 200 includes a plurality ofbond gap control structures 210 adjacent the outer perimeter of the capsealing rings 204. Again, the bond gap control structures 210 serve as amechanical stop that controls the thickness of a bond line between twojoined surfaces. In the embodiment illustrated, the bond gap controlstructures 210 are schematically depicted as single structures disposedin a y-axis direction with respect to FIG. 2, whereas the bonding padchannels 208 are generally disposed in an x-axis direction with respectto FIG. 2. However, other arrangements are also possible with respect tothe cap wafer 200.

For example, FIG. 3 is an enlarged top view of a patterned side of anexemplary cap wafer 300 that may also be used in accordance with theteachings herein. For ease of illustration, like reference numbers withrespect to FIG. 2 are used in FIG. 3. As is shown in the more detailedview of FIG. 3, the substrate 202 has saw lines 302 depictedapproximately in the center of scribe regions 304 where the substrate202 is to be cut. In this embodiment, a plurality of BGCSs 210 aredisposed within the scribe regions 304, in both the x-axis and y-axisdirections to operate as a mechanical stop that controls the geometry ofa bond line of a cap sealing ring 204. In an exemplary embodiment, theBGCS may only need to be disposed in either the x-axis or y-axisdirections. The geometry of a bond line includes both gap thickness andwidth. The gap refers to the gap between bonded substrates, wherein thegap thickness is measured in a direction that is perpendicular to theflat surface of the substrate 202. The width is measured along the flatsurface of substrate 202. A BGCS 210 may have any suitable size andshape. For example, each BGCS 210 may have a width in any of thefollowing ranges 1 to 10, 10 to 50, 50 to 100, or over 100 microns (μm),a length in any of the following ranges 50 to 100, 100 to 200, or over200 μm, and a thickness in any of the following ranges 1 to 5, 5 to 10,10 to 20, or over 20.

Referring now to FIG. 4, there is shown a side cross sectional view of aportion of a device wafer 400 to be bonded to a corresponding portion ofa cap wafer 200. Again, for ease of illustration, like reference numberswith respect to the cap wafers of FIGS. 2 and 3 are used in FIG. 4. Asdepicted in FIG. 4, the cap wafer 200 is shown in a bottom, cavity-uporientation and includes the substrate 202, etched out cavity 206, and acap sealing ring 204 a that surrounds the cavity 206. Adjacent sealingrings 204 b are also shown for adjacent cavities on the cap wafer 202for illustrative purposes. A cap wafer portion of each BGCS 210 is alsoillustrated on the cap wafer 200 in FIG. 4.

As indicated above, in contrast to using special materials to formBGCSs, the BGCSs are instead formed using existing materials for boththe cap wafer 200 and the device wafer 400. In the case of the cap wafer200, a first layer for the BGCS 210 may include an antireflective (AR)coating layer 402 also formed on the thinned portions of the substrate202 (i.e., corresponding to locations of the cavities 206 that willcover the corresponding MEMS devices on the device wafer 400), inaccordance with the fabrication of infrared detectors or other suchoptical devices. In an exemplary embodiment, the AR portion of the BGCS210 may have a thickness on the order of about 5.5 μm to about 8.0 μm,and more specifically about 7.0 μm. In order to form the AR coatinglayer 402 at the BGCS locations, in addition to the existing locationson the cap wafer, the applicable patterning mask(s) are modified so thatthe AR material remains in the BGCS locations.

In addition, a second layer for the BGCS 210 may include a solder basemetal stack layer 404 that is also used as a solder base for the sealingrings 204 a, 204 b. The solder metal stack layer may include, forexample, a layer of titanium (Ti), followed by a layer of nickel (Ni),and followed by a layer of gold (Au). Other metals, however, may also beused. The combined metal stack layer 404 may have an exemplary thicknesson the order of about 0.4 μm to about 0.8 μm, and more specificallyabout 0.6 μm. The formation of the cap wafer is completed with theaddition of an appropriate solder metal layer 406 atop the metal stacklayer 404 of the sealing rings 204 a, 204 b. If a sealing method otherthan heat activated solder is used, solder metal layer 406 is replacedby a material selected to obtain a vacuum tight seal. The solder metallayer 406 may be deposited through traditional integrated circuitfabrication techniques or other suitable deposition processes including,but not limited to, electroplating, electroless plating, and vacuumdeposition.

Turning now to the device wafer 400, a substrate wafer 410 (e.g.,silicon) has a plurality of IC devices 412 formed thereon. The ICdevices 412 may be MEMS devices such as a bolometer, for example, formedusing traditional methods of integrated circuit fabrication. Althoughthe present embodiment is discussed in terms of vacuum packaging forMEMS devices, the principles disclosed herein may be applied to vacuumpackaging of any integrated circuit device, or similar device, formed ona substrate material and contained within a vacuum package. Each ICdevice 412 is configured to be aligned with a corresponding cavity 206on the cap wafer 200. As is the case with the cap wafer 200, the devicewafer 400 may be formed with one or more materials that match up withmaterials on the cap wafer 200 to formed integrated BGCSs. In FIG. 4, adevice wafer portion of each BGCS is indicated at 414. That is, thedevice wafer portion 414 of a BGCS and the cap wafer portion 210 of aBGCS are mated to form an integrated BGCS, as shown hereinafter.

With respect to the device wafer 400, a first layer for the device waferportion 414 of a BGCS may include a sacrificial polyimide layer 416 thatis used to thermally isolate the IC device 412 (e.g., bolometer) fromthe substrate 410. In this sense, the polyimide layer 416 is notsacrificial in the BGCS regions, in that that layer patterning isadjusted such that the polyimide remains to contribute to the overallBGCS thickness. In an exemplary embodiment, the polyimide layer 416 mayhave a thickness on the order of about 1.8 μm to about 2.0 μm.

As is the also case with the cap wafer 200, the device wafer 400 isprovided with a solder base metal stack layer 418 that is used as asolder base to mate with the solder metal 406 atop the metal stack layer404 of the sealing rings 204 a, 204 b. The solder metal stack layer 418may also include a Ti/Ni/Au stack similar to stack 404, and at asubstantially same thickness. In addition to serving as a solder basefor sealing rings on the device wafer, the metal stack layer 418 mayalso serve as a second layer for the device wafer portion 414 of a BGCS.As particularly illustrated in FIG. 4, patterning of the metal stacklayer 418 is such that it covers not only the top surface of thepolyimide layer 416, but also the sidewall surfaces thereof.

With both the cap wafer 200 and device wafer 400 configured as depictedin FIG. 4, the arrangement is ready for final assembly. To prepare theassembly, the cap wafer 200 may be placed in an assembly holder (notshown) with the solder layer 406 facing up. The device wafer 400 isaligned over the cap wafer 200 such that the metal stack layers 418(i.e., not the metal stack layers 418 that are part of the integratedBGCS) are aligned over the corresponding cap wafer sealing rings 204 a,204 b.

FIG. 5 depicts the joining of the cap wafer 200 with the device wafer400 to form an assembly 500. As can be seen, an integrated BGCSindicated at the circled region 502 is defined by the combined materialstack that includes the AR and solder metal layer 402, 404, respectivelyfrom the cap wafer 200 and the solder metal layer and polyimide layers418, 416, respectively, from the device wafer 400. The integrated BGCSs,like previous spacers, allow for good solder bond width and gapuniformity characteristics for the now-formed bond lines 504 in FIG. 5,but without the need to form the BGCSs using additional materials nototherwise used in forming either the cap wafer 200 or the device wafer400. In total, the bond lines may have an exemplary thickness on theorder of about 10 μm as result of the combined thicknesses of the AR,polyimide and metal layers left in the scribe regions of the cap anddevice wafers.

After any appropriate testing of the MEMS devices 12, the assembly 500is diced by sawing along, for example, a saw line 302 such as shown inFIG. 3, which may or may not result in the removal of the integratedBGCS shown at 502 in FIG. 5. The dicing of the assembly 500 may beaccomplished by using traditional methods of dicing semiconductor waferswith completed integrated circuits. By vacuum packaging MEMS devices 412at the wafer level, traditional methods of handling integrated circuitdevices may be used since the vacuum package provides protection to thedelicate MEMS device 412. A completed die representing a vacuum packagedMEMS device 412 may be mounted by chip-on-board methods or injectionmolded into a plastic package (not shown). In addition, a completed diemay be placed in a non-vacuum package with other components (not shown).

Although the integrated BGCSs 502 in FIG. 5 is shown disposed in orproximate to a scribe region in between adjacent bond lines 504, it isalso contemplated that the BGCSs 502 may also be positioned inadditional locations. For example, the BGCS materials from the cap wafer200 and device wafer 400 could be patterned such that one or more BGCSs502 reside within the confines of the sealed cavity, such as at location506 for example. In this case, the BGCS 502 would remain as part of thecompleted product, after dicing.

Referring now to FIG. 6, there is shown a side cross sectional view of aportion of a device wafer 400 to be bonded to a corresponding portion ofa cap wafer 200 that results in the formation of integrated BGCSs, inaccordance with another exemplary embodiment. In this embodiment, anadditional layer used in the processing of the cap wafer is alsointentionally left in the scribe region of the substrate 202 in order tocontribute to the overall thickness of the BGCS. More specifically, thecap wafer 200 includes a vacuum getter layer 602 initially formed on theinside surfaces of the cap substrate 202 over the AR layer,corresponding to the etched cavity regions 206. Generally, a getter is adeposit of reactive material that is placed inside a vacuum system, forthe purpose of completing and maintaining the vacuum. When gas moleculesstrike the getter material, the molecules combine with the getterchemically or by adsorption, removing small amounts of gas from theevacuated space. The getter layer 602 may include one or more layers ofelements such as titanium, zirconium, iron, and vanadium, to name a fewexamples.

As further seen in FIG. 6, the getter layer 602 is left remaining atopthe AR and solder base metal layers 402, 404, respectively, to become apart of the cap wafer portion of each BGCS 210. In the bonded view ofFIG. 7, the assembly 700 includes integrated BGCSs, indicated by thedashed circled region 702. In an exemplary embodiment, the getter layer602 may have a thickness on the order of about 0.3 μm to about 2.0 μm,and more specifically about 0.9 μm. As such, the embodiment of FIGS. 6and 7, which uses the additional getter layer 602 in forming a BGCS, mayprovide for an additional bond line thickness of about 1.0 μm or morewith respect to the embodiment of FIGS. 4 and 5.

In order to achieve a desired plateau width for the portions of thegetter layer 602 that become a part of the BGCSs, an allowance may bemade for shadowing of the getter deposition mask, as more particularlyillustrated in FIGS. 8 and 9. In the top view of FIG. 8, referencenumber 802 depicts a width of a saw lane on the scribe region of the capwafer substrate. The saw lane 802 may be on the order of about 480 μm.Region 804 represents the solder metal stack portion of the BGCS thatcovers the top and sidewall surfaces of the AR layer (not shown in FIG.8). Region 806 represents the getter layer portion of the BGCS thatoverlaps the top surface or plateau of the solder base metal, which isdepicted by the dashed line 808. In an embodiment, an exemplary width810 of a shadowed edge overlap of the getter layer is on the order ofabout 40 μm.

FIG. 9 is a cross sectional, perspective view illustrating the placementof the vacuum getter layer 806 atop the solder metal layer stack 804 ofFIG. 8. In this view, the AR layer depicted by region 902 is shown. Thedashed lines 904 represent regions of a getter shadow mask, wherein aspacing 906 between the regions (i.e., the shadow mask opening width)represents the plateau width of the top of the solder metal stack 804plus the shadowed edge width 810.

In the embodiments described above, the BGCSs are formed using existingmaterials for both the cap wafer 200 and the device wafer 400. However,it is also contemplated that the BGCS material could be formed fromexisting layers on either the cap wafer 200 alone or on the wafer layer400 alone. In such a case, the overall thickness of the BGCSs may bereduced and/or in the alternative, the existing layers used to form thecap wafer 200 or the device wafer 400 may be formed at a greater initialthickness so as to compensate for the BGCS material being formed on onlyone of the two wafers.

By way of example, FIG. 10 is a side cross sectional view of a portionof a device wafer 400 to be bonded to a corresponding portion of a capwafer 200 that results in the formation of integrated BGCSs, inaccordance with another exemplary embodiment. In this embodiment, theBCGS layer(s) are formed only on the cap wafer 200. Here, the layer(s)are generally denoted at 1000, and may include one or more of thespecific layers previously described as being formed on the cap wafer200 such as, for example, AR layers, solder base metal stack layers, andgetter layers. In the bonded view of FIG. 11, the BCGS layer(s) 1000serve as the entire integrated BGCSs for the assembly 1100. Again, aswith the previous embodiments, the integrated BGCSs 1000 may be locatedelsewhere besides the scribe regions.

Conversely, FIG. 12 is a side cross sectional view of a portion of adevice wafer 400 to be bonded to a corresponding portion of a cap wafer200 that results in the formation of integrated BGCSs, in accordancewith another exemplary embodiment. In this embodiment, the BCGS layer(s)are formed only on the device wafer 400. The BGCS layer(s) are generallydenoted at 1200, and may include one or more of the specific layerspreviously described as being formed on the cap wafer 400 such as, forexample, solder base metal stack layers and polyimide layers. In thebonded view of FIG. 13, the BCGS layer(s) 1200 serve as the entireintegrated BGCSs for the assembly 1300.

As will thus be appreciated, among the technical benefits of the abovedescribed embodiments is the elimination of added processing steps tofabricate bond gap control spacers from materials that are not used inthe preparation of device or cap wafer structures. Fewer processingsteps in turn results in cost reduction and less chance for yield loss.Rather, the BGCS material is advantageous taken from existing layersformed on the cap and/or device wafers that would ordinarily be removedfrom (or not initially formed in) the scribe regions of the wafers. Suchexemplary materials include, but are not necessarily limited to, ARcoatings, solder base metals, polyimides and vacuum getter layers.

While the disclosure has been described with reference to a preferredembodiment or embodiments, it will be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the scope of the disclosure.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the disclosure withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the disclosure not be limited to the particular embodimentdisclosed as the best mode contemplated for carrying out thisdisclosure, but that the disclosure will include all embodiments fallingwithin the scope of the appended claims.

The invention claimed is:
 1. A wafer level packaged circuit device,comprising: a device wafer bonded to a cap wafer; the device waferincluding a polyimide layer formed in a first region of a substrate ofthe device wafer, and a first solder metal stack layer formed on thepolyimide layer, wherein the polyimide layer is a same polyimide layerthat is also used in the formation of an integrated circuit on thedevice wafer, and the first solder metal stack layer is also a samefirst solder metal stack layer used to form a sealing ring for thedevice wafer; the cap wafer including an antireflective coating layerformed in a second region of a substrate of the cap wafer, and a secondsolder metal stack layer formed on the antireflective coating layer,wherein the antireflective coating layer is a same antireflectivecoating layer that is also formed on a cavity portion of the cap wafer,and the second solder metal stack layer is also a same second soldermetal stack layer used to form a sealing ring for the cap wafer; and anintegrated bond gap control structure (BGCS) disposed between the devicewafer and the cap wafer, the integrated BGCS comprising the polyimidelayer, the first solder metal stack layer, the second solder metal stacklayer, and the antireflective coating layer.
 2. The device of claim 1,wherein: the cap wafer further comprises a vacuum getter layer formed onthe second solder metal stack layer, wherein the vacuum getter layer isa same vacuum getter layer that is also formed on the antireflectivecoating layer of the cavity portion of the cap wafer; and wherein theintegrated bond gap control structure comprises the polyimide layer, thefirst solder metal stack layer, the vacuum getter layer, the secondsolder metal stack layer, and the antireflective coating layer.
 3. Thedevice of claim 1, wherein the first and solder metal stack layerscomprise a titanium/nickel/gold stack layers.
 4. The device of claim 1,wherein the integrated bond gap control structure has a thickness on theorder of about 10 microns (μm).
 5. The device of claim 1, wherein: thepolyimide layer has a thickness on the order of about 1.0 microns (μm)to about 2.0 μm; the first solder metal stack layer has a thickness onthe order of about 0.4 μm to about 0.8 μm; the vacuum getter layer has athickness on the order of about 0.3 μm to about 2.0 μm; the secondsolder metal stack layer has a thickness on the order of about 0.4 μm toabout 0.8 μm; and the antireflective coating layer has a thickness onthe order of about 5.5 μm to about 8.0 μm.
 6. The device of claim 1,wherein the first region corresponds to a scribe region of the devicewafer and the second region corresponds to a scribe region of the capwafer.